By using the term "pious youth" the poet addresses only one person. That person is Miss Phillis Wheatley.
Through questions similar to yours, we can see your question refers to the poem "Address to Miss Phillis Wheatley," written by Jupiter Hammon.
We can arrive at this answer because:
Hammon wanted to talk to Wheatley because they were both African Americans and he believed they should celebrate that. Also, he was very happy to know that Wheatley was a Christian, like him.
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